Pulsed waveguide sensing device and method for measuring a parameter

ABSTRACT

At least one embodiment is directed to a sensor for measuring a parameter. A signal path of the system comprises an amplifier ( 612 ), a sensor element, and an amplifier ( 620 ). The sensor element comprises a transducer ( 4 ), a waveguide ( 5 ), and a transducer ( 30 ). A parameter such as force or pressure applied to the sensor element can change the length of waveguide ( 5 ). A pulsed energy wave is emitted by the transducer ( 4 ) into the waveguide ( 5 ) at a first location. The transducer ( 30 ) is responsive pulsed energy waves at a second location of the waveguide ( 5 ). The transit time of each pulsed energy wave is measured. The transit time corresponds to the pressure or force applied to the sensor element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. provisional patentapplications No. 61/221,761, 61/221,767, 61/221,779, 61/221,788,61/221,793, 61/221,801, 61/221,808, 61/221,817, 61/221,867, 61/221,874,61/221,879, 61/221,881, 61/221,886, 61/221,889, 61/221,894, 61/221,901,61/221,909, 61/221,916, 61/221,923, and 61/221,929 all filed 30 Jun.2009. The disclosures of which are incorporated herein by reference inits entirety.

FIELD

The disclosure relates in general to measurement, and particularlythough not exclusively, is related to a structure and method to measurea parameter.

BACKGROUND

Sensors are used to provide information to a device or system. Thesensor information can be critical to device operation or provideadditional data on the system or an external environment. For example, atemperature sensor is commonly used to monitor the operating temperatureof components. The temperature sensor can be used to monitor averageoperating temperatures and instantaneous operating extremes. Sensor datacan be used to understand how device functions or performs in differentworking environments, users, and environmental factors. Sensors cantrigger an action such as turning off the system or modifying operationof the system in response to a measured parameter.

In general, cost typically increases with the measurement precision ofthe sensor. Cost can limit the use of highly accurate sensors in pricesensitive applications. Furthermore, there is substantial need for lowpower sensing that can be used in systems that are battery operated.Ideally, the sensing technology used in a low power applications willnot greatly affect battery life. Moreover, a high percentage ofbattery-operated devices are portable devices comprising a small volumeand low weight. Device portability can place further size and weightconstraints on the sensor technology used. Thus, form factor, powerdissipation, cost, and measurement accuracy are important criteria thatare evaluated when selecting a sensor for a specific application.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is an illustration of a sensor module subjected to a parameter inaccordance with an exemplary embodiment;

FIG. 2 is a simplified cross-sectional view of a sensing module inaccordance with an exemplary embodiment;

FIG. 3 is an exemplary assemblage for illustrating reflectance andunidirectional modes of operation;

FIG. 4 is an exemplary assemblage that illustrates propagation ofultrasound waves within a waveguide in the bi-directional mode ofoperation of this assemblage;

FIG. 5 is an exemplary cross-sectional view of a sensor element toillustrate changes in the propagation of ultrasound waves with changesin the length of a waveguide;

FIG. 6 is an exemplary block diagram of a positive feedback closed-loopmeasurement system in accordance with an exemplary embodiment; and

FIG. 7 is measurement system operating in a pulsed mode with digitaloutput according to one embodiment;

FIG. 8 is a timing diagram of a measurement system in accordance with anexemplary embodiment;

FIG. 9 is an exemplary block diagram of the components of a sensingmodule;

FIG. 10 depicts a cross sectional view of a sensing module in furtherdetail according to one embodiment; and

FIG. 11 is a communication network 1100 for sensing applications inaccordance with an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description of exemplary embodiment(s) is merelyillustrative in nature and is in no way intended to limit the invention,its application, or uses.

Processes, techniques, apparatus, and materials as known by one ofordinary skill in the art may not be discussed in detail but areintended to be part of the enabling description where appropriate. Forexample specific computer code may not be listed for achieving each ofthe steps discussed, however one of ordinary skill would be able,without undo experimentation, to write such code given the enablingdisclosure herein. Such code is intended to fall within the scope of atleast one exemplary embodiment.

Additionally, the sizes of structures used in exemplary embodiments arenot limited by any discussion herein (e.g., the sizes of structures canbe macro (centimeter, meter, and larger sizes), micro (micrometer), andnanometer size and smaller).

Notice that similar reference numerals and letters refer to similaritems in the following figures, and thus once an item is defined in onefigure, it may not be discussed or further defined in the followingfigures.

In all of the examples illustrated and discussed herein, any specificvalues, should be interpreted to be illustrative only and non-limiting.Thus, other examples of the exemplary embodiments could have differentvalues.

FIG. 1 is an illustration of a sensor 100 in accordance with anexemplary embodiment. Sensor 100 is placed in a position where aparameter to measured can be applied to the device or affects thedevice. In a non-limiting example, a force or pressure is used toillustrate measuring a parameter using sensor 100. Sensor 100 is placedbetween a surface 102 and a surface 106 of object 104. A compressiveforce is applied to sensor 100. In general, embodiments of sensor 100are broadly directed to measurement of physical parameters, and moreparticularly, to evaluating changes in the transit time of a pulsedenergy wave propagating through a medium.

In at least one exemplary embodiment, an energy pulse is directed withinone or more waveguides in sensor 100 by way of pulse mode operations andpulse shaping. The waveguide is a conduit that directs the energy pulsein a predetermined direction. The energy pulse is typically confinedwithin the waveguide. A transit time of an energy pulse through a mediumis related to the material properties of the medium. This relationshipis used to generate accurate measurements of parameters such asdistance, weight, strain, pressure, wear, vibration, viscosity, anddensity to name but a few.

Sensor 100 can be size constrained by form factor requirements offitting within a region of a device or system. In a non-limitingexample, sensor 100 is used as an aid in a tool that is both size andcost constrained. In one embodiment, sensor 100 can be fitted in acavity of a tool having a surface exposed or coupled to a component ofthe tool that opposes a surface to which a pressure or force is applied.For example, sensor 100 can be used in a dental drill to measure thepressure applied on a tooth thereby providing indication of an optimalpressure for removing material especially when the material is thin ordelicate. The mechanical portion of sensor 100 comprises a stack of afirst transducer, a medium, and a second transducer. The stack can bemade very thin depending on the application, the parameter to bemeasured, and the range of measurement. The small form factor allows itto be used on many existing devices that currently do not have sensingcapability. Moreover, a pulsed sensing methodology is used thatminimizes power consumption. Thus, power usage by sensor 100 can be madevery low making it useful for devices having a temporary power source orbattery operated devices.

In the example, sensor 100 can utilize more than one sensor stack. Usingmore than one sensor stack allows positional information to be provided.Sensor 100 can monitor where surface 106 of object 104 contacts themajor surface of sensor 100. In one embodiment, the sensor stacks are inpredetermined positions underlying the major surface of sensor 100.Force measurements in conjunction with the predetermined positions ofeach sensor stack is used to determine the point or region of contact byobject 104 via force differentials. The electronics of sensor 100 can bewithin the sensor housing or external to the sensor housing. In oneembodiment, data from sensor 100 is transmitted to a receiving station110 via wired or wireless communications. The receiving station 110 caninclude data processing, storage, or display, or combination thereof andprovide real time graphical representation of the level and distributionof the load. Receiving station 110 can record and provide accountinginformation of sensor 100 to an appropriate authority. In a furtherembodiment, sensor 100 is a disposable system. Sensor 100 can be used asa low cost disposable measuring system that reduces capitalexpenditures, maintenance, and accounting when compared to permanentmeasurement systems.

Sensor 100 can measure forces (Fx, Fy, Fz) with corresponding locationsand torques (e.g. Tx, Ty, and Tz) on the object 104 and the surface 102.The measured force and torque data is transmitted to receiving station110 to provide real-time visualization for assisting the user inidentifying any adjustments needed to achieve pressure and positioning.The data has substantial value in determining ranges of load andalignment tolerances required to minimize rework and optimize systemperformance.

FIG. 2 is a simplified cross-sectional view of a sensing module 101 (orassemblage in accordance with an exemplary embodiment. The sensingmodule (or assemblage) is an electro-mechanical assembly comprisingelectrical components and mechanical components that when configured andoperated in accordance with a sensing mode performs as a positivefeedback closed-loop measurement system. The measurement system canprecisely measure applied forces, such as loading, and location on theelectro-mechanical assembly.

In one embodiment, the electrical components can include ultrasoundresonators or transducers, ultrasound waveguides, and signal processingelectronics, but are not limited to these. The mechanical components caninclude biasing springs 32, spring retainers and posts, and loadplatforms 6, but are not limited to these. The electrical components andmechanical components can be inter-assembled (or integrated) onto aprinted circuit board 36 to operate as a coherent ultrasonic measurementsystem within sensing module 101 and according to the sensing mode. Aswill be explained hereinbelow in more detail, the signal processingelectronics incorporate edge detect circuitry that detects an edge of asignal after it has propagated through waveguide 5. The detectioninitiates the generation of a new pulse by an ultrasound resonator ortransducer that is coupled to waveguide 5 for propagation therethrough.A change in transit time of a pulse through waveguide 5 is measured andcorrelates to a change in material property of waveguide 5.

Sensing module 101 comprises one or more assemblages 3 each comprisedone or more ultrasound resonators. As illustrated, waveguide 5 iscoupled between transducers 4 and 30 and affixed to load bearing orcontacting surfaces 6. In one exemplary embodiment, an ultrasound signalis coupled for propagation through waveguide 5. The sensing module 101is placed, attached to, or affixed to, or within a body, instrument, orother physical system 7 having a member or members 8 in contact with theload bearing or contacting surfaces 6 of the sensing module 101. Thisarrangement facilitates translating the parameters of interest intochanges in the length or compression or extension of the waveguide orwaveguides 5 within the sensing module or device 100 and convertingthese changes in length into electrical signals. This facilitatescapturing data, measuring parameters of interest and digitizing thatdata, and then subsequently communicating that data through antenna 34to external equipment with minimal disturbance to the operation of thebody, instrument, appliance, vehicle, equipment, or physical system 7for a wide range of applications.

The sensing module 101 supports three modes of operation of pulsepropagation and measurement: reflectance, unidirectional, andbi-directional. These modes can be used as appropriate for eachindividual application. In unidirectional and bi-directional modes, achosen ultrasound resonator or transducer is controlled to emit pulsesof ultrasound waves into the ultrasound waveguide and one or more otherultrasound resonators or transducers are controlled to detect thepropagation of the pulses of ultrasound waves at a specified location orlocations within the ultrasound waveguide. In reflectance or pulse-echomode, a single ultrasound or transducer emits pulses of ultrasound wavesinto waveguide 5 and subsequently detects pulses of echo waves afterreflection from a selected feature or termination of the waveguide. Inpulse-echo mode, echoes of the pulses can be detected by controlling theactions of the emitting ultrasound resonator or transducer to alternatebetween emitting and detecting modes of operation. Pulse and pulse-echomodes of operation may require operation with more than one pulsedenergy wave propagating within the waveguide at equilibrium.

Many parameters of interest within physical systems or bodies can bemeasured by evaluating changes in the transit time of energy pulses. Thefrequency or instantaneous frequency, is the reciprocal of a single timeperiod or an average of more than one time period of the discontinuoussignal. The type of the energy pulse used is determined by factors suchas distance of measurement, medium in which the signal travels, accuracyrequired by the measurement, precision required by the measurement, formfactor, power constraints, and cost. In the non-limiting example, pulsesof ultrasound energy provide accurate markers for measuring transit timeof the pulses within waveguide 5. In general, an ultrasonic signal is anacoustic signal having a frequency above the human hearing range(e.g. >20 KHz) including frequencies well into the megahertz range. Inone embodiment, a change in transit time of an ultrasonic energy pulsecorresponds to a difference in the physical dimension of the waveguidefrom a previous state. For example, a force or pressure applied acrosswaveguide 5 reduces the length of waveguide 5 thereby changing thetransit time of the energy pulse When integrated as a sensing module andinserted or coupled to a physical system or body, these changes aredirectly correlated to the physical changes on the system or body andcan be readily measured as a pressure or a force.

FIG. 3 is an exemplary assemblage 200 for illustrating reflectance andunidirectional modes of operation. It comprises one or more transducers202, 204, and 206, one or more waveguides 214, and one or more optionalreflecting surfaces 216. The assemblage 200 illustrates propagation ofultrasound waves 218 within the waveguide 214 in the reflectance andunidirectional modes of operation. Either ultrasound resonator ortransducer 202, 204, and 206 in combination with interfacing material ormaterials 208, 210, and 212 if required, can be selected to emitultrasound waves 218 into the waveguide 214.

In unidirectional mode, either of the ultrasound resonators ortransducers for example 202 can be enabled to emit ultrasound waves 218into the waveguide 214. The non-emitting ultrasound resonator ortransducer 204 is enabled to detect the ultrasound waves 218 emitted bythe ultrasound resonator or transducer 202.

In reflectance mode, the ultrasound waves 218 are detected by theemitting ultrasound resonator or transducer 202 after reflecting from asurface, interface, or body at the opposite end of the waveguide 214. Inthis mode, either of the ultrasound resonators or transducers 202 or 204can be selected to emit and detect ultrasound waves. Additionalreflection features 216 can be added within the waveguide structure toreflect ultrasound waves. This can support operation in a combination ofunidirectional and reflectance modes. In this mode of operation, one ofthe ultrasound resonators, for example resonator 202 is controlled toemit ultrasound waves 218 into the waveguide 214. Another ultrasoundresonator or transducer 206 is controlled to detect the ultrasound waves218 emitted by the emitting ultrasound resonator 202 (or transducer)subsequent to their reflection by reflecting feature 216.

FIG. 4 is an exemplary assemblage 300 that illustrates propagation ofultrasound waves 310 and 318 within the waveguide 306 in thebi-directional mode of operation of this assemblage. In this mode, theselection of the roles of the two individual ultrasound resonators (302,304) or transducers affixed to interfacing material 320 and 322, ifrequired, are periodically reversed. In the bi-directional mode, thetransit time of ultrasound waves propagating in either direction withinthe waveguide 306 can be measured. This can enable adjustment forDoppler effects in applications where the sensing module 308 isoperating while in motion 316. Furthermore, this mode of operation helpsassure accurate measurement of the applied load, force, pressure, ordisplacement by capturing data for computing adjustments to offset thisexternal motion 316. An advantage is provided in situations wherein thebody, instrument, appliance, vehicle, equipment, or other physicalsystem 314, is itself operating or moving during sensing of load,pressure, or displacement. Similarly, the capability can also correct insituation where the body, instrument, appliance, vehicle, equipment, orother physical system, is causing the portion 312 of the body,instrument, appliance, vehicle, equipment, or other physical systembeing measured to be in motion 316 during sensing of load, force,pressure, or displacement. Other adjustments to the measurement forphysical changes to system 314 are contemplated and can be compensatedfor in a similar fashion. For example, temperature of system 314 can bemeasured and a lookup table or equation having a relationship oftemperature versus transit time can be used to normalize measurements.Differential measurement techniques can also be used to cancel manytypes of common factors as is known in the art.

The use of waveguide 306 enables the construction of low cost sensingmodules and devices over a wide range of sizes, including highly compactsensing modules, disposable modules for bio-medical applications, anddevices, using standard components and manufacturing processes. Theflexibility to construct sensing modules and devices with very highlevels of measurement accuracy, repeatability, and resolution that canscale over a wide range of sizes enables sensing modules and devices tothe tailored to fit and collect data on the physical parameter orparameters of interest for a wide range of medical and non-medicalapplications.

For example, sensing modules or devices may be placed on or within, orattached or affixed to or within, a wide range of physical systemsincluding, but not limited to instruments, appliances, vehicles,equipments, or other physical systems as well as animal and humanbodies, for sensing the parameter or parameters of interest in real timewithout disturbing the operation of the body, instrument, appliance,vehicle, equipment, or physical system.

In addition to non-medical applications, examples of a wide range ofpotential medical applications may include, but are not limited to,implantable devices, modules within implantable devices, modules ordevices within intra-operative implants or trial inserts, modules withininserted or ingested devices, modules within wearable devices, moduleswithin handheld devices, modules within instruments, appliances,equipment, or accessories of all of these, or disposables withinimplants, trial inserts, inserted or ingested devices, wearable devices,handheld devices, instruments, appliances, equipment, or accessories tothese devices, instruments, appliances, or equipment. Many physiologicalparameters within animal or human bodies may be measured including, butnot limited to, loading within individual joints, bone density,movement, various parameters of interstitial fluids including, but notlimited to, viscosity, pressure, and localized temperature withapplications throughout the vascular, lymph, respiratory, and digestivesystems, as well as within or affecting muscles, bones, joints, and softtissue areas. For example, orthopedic applications may include, but arenot limited to, load bearing prosthetic components, or provisional ortrial prosthetic components for, but not limited to, surgical proceduresfor knees, hips, shoulders, elbows, wrists, ankles, and spines; anyother orthopedic or musculoskeletal implant, or any combination ofthese.

FIG. 5 is an exemplary cross-sectional view of a sensor element 400 toillustrate changes in the propagation of ultrasound waves 414 withchanges in the length of a waveguide 406. In general, measurement of aparameter is achieved by relating displacement to the parameter. In oneembodiment, the displacement required over the entire measurement rangeis measured in microns. For example, an external force 408 compresseswaveguide 406 thereby changing the length of waveguide 406. Sensingcircuitry (not shown) measures the propagation characteristics ofultrasonic signals in the waveguide 406 to determine the change in thelength of the waveguide 406. These changes in length change in directproportion to the parameters of interest thus enabling the conversion ofchanges in the parameter or parameters of interest into electricalsignals.

As illustrated, external force 408 compresses waveguide 406 and pushesthe transducers 402 and 404 closer to one another by a distance 410.This changes the length of waveguide 406 by distance 412 of thewaveguide propagation path between transducers 402 and 404. Depending onthe operating mode, the sensing circuitry measures the change in lengthof the waveguide 406 by analyzing characteristics of the propagation ofultrasound waves within the waveguide.

One interpretation of FIG. 5 illustrates waves emitting from transducer402 at one end of waveguide 406 and propagating to transducer 404 at theother end of the waveguide 406. The interpretation includes the effectof movement of waveguide 406 and thus the velocity of waves propagatingwithin waveguide 406 (without changing shape or width of individualwaves) and therefore the transit time between transducers 402 and 404 ateach end of the waveguide. The interpretation further includes theopposite effect on waves propagating in the opposite direction and isevaluated to estimate the velocity of the waveguide and remove it byaveraging the transit time of waves propagating in both directions.

Changes in the parameter or parameters of interest are measured bymeasuring changes in the transit time of energy pulses or waves withinthe propagating medium. Closed loop measurement of changes in theparameter or parameters of interest is achieved by modulating therepetition rate of energy pulses or the frequency of energy waves as afunction of the propagation characteristics of the elastic energypropagating structure.

These measurements may be implemented with an integrated wirelesssensing module or device having an encapsulating structure that supportssensors and load bearing or contacting surfaces and an electronicassemblage that integrates a power supply, sensing elements, energytransducer or transducers and elastic energy propagating structure orstructures, biasing spring or springs or other form of elastic members,an accelerometer, antennas and electronic circuitry that processesmeasurement data as well as controls all operations of ultrasoundgeneration, propagation, and detection and wireless communications. Theelectronics assemblage also supports testability and calibrationfeatures that assure the quality, accuracy, and reliability of thecompleted wireless sensing module or device.

FIG. 6 is an exemplary block diagram 500 of a positive feedbackclosed-loop measurement system in accordance with one embodiment. Themeasurement system comprises components of the sensing module 101 shownin FIG. 2. The measurement system includes a sensing assemblage 502 anda pulsed system 504 that detects energy waves 506 in one or morewaveguides 5 of the sensing assembly 502. A pulse 520 is generated inresponse to the detection of energy waves 506 to initiate a propagationof a new pulse in waveguide 5.

The sensing assembly 502 comprises transducer 4, transducer 30, and awaveguide 5 (or energy propagating structure). In a non-limitingexample, sensing assemblage 502 is affixed to load bearing or contactingsurfaces 508. External forces applied to the contacting surfaces 508compress the waveguide 5 and change the length of the waveguide 5. Thetransducers 4 and 30 will also be moved closer together. The change indistance affects the transmit time 510 of energy waves 506 transmittedand received between transducers 4 and 30. The pulsed system 504 inresponse to these physical changes will detect each energy wave sooner(e.g. shorter transit time) and initiate the propagation of new pulsesassociated with the shorter transit time. As will be explained below,this is accomplished by way of pulse system 504 in conjunction with thepulse circuit 512, the mode control 514, and the edge detect circuit516.

Notably, changes in the waveguide 5 (energy propagating structure orstructures) alter the propagation properties of the medium ofpropagation (e.g. transmit time 510). A pulsed approach reduces powerdissipation allowing for a temporary power source such as a battery orcapacitor to power the system during the course of operation. In atleast one exemplary embodiment, a pulse is provided to transducer 4coupled to a first surface of waveguide 5. Transducer 4 generates apulsed energy wave 506 coupled into waveguide 5. In a non-limitingexample, transducer 4 is a piezoelectric device capable of transmittingand receiving acoustic signals in the ultrasonic frequency range.

Transducer 30 is coupled to a second surface of waveguide 5 to receivethe propagated pulsed signal and generates a corresponding electricalsignal. The electrical signal output by transducer 30 is coupled to edgedetect circuit 516. In at least one exemplary embodiment, edge detectcircuit 516 detects a leading edge of the electrical signal output bytransducer 30 (e.g. the propagated energy wave 506 through waveguide 5).The detection of the propagated pulsed signal occurs earlier (due to thelength/distance reduction of waveguide 5) than a signal prior toexternal forces 508 being applied to sensing assemblage 502. Pulsecircuit 512 generates a new pulse in response to detection of thepropagated pulsed signal by edge detect circuit 516. The new pulse isprovided to transducer 4 to initiate a new pulsed sequence. Thus, eachpulsed sequence is an individual event of pulse propagation, pulsedetection and subsequent pulse generation that initiates the next pulsesequence.

The transit time 510 of the propagated pulse corresponds to the timefrom the detection of one propagated pulse to the next propagated pulse.There is delay associated with each circuit described above. Typically,the total delay of the circuitry is significantly less than thepropagation time of a pulsed signal through waveguide 5. In addition,variation in circuit delay is minimal under equilibrium conditions.Multiple pulse to pulse timings can be used to generate an average timeperiod when change in external forces 508 occur relatively slowly inrelation to the pulsed signal propagation time such as in a physiologicor mechanical system. The digital counter 518 in conjunction withelectronic components counts the number of propagated pulses todetermine a corresponding change in the length of the waveguide 5. Thesechanges in length change in direct proportion to the external force thusenabling the conversion of changes in parameter or parameters ofinterest into electrical signals.

One method of operation holds the number of pulsed energy wavespropagating through waveguide 5 as a constant integer number. A timeperiod of a pulsed energy wave corresponds to the time between theleading pulse edges of adjacent pulsed energy waves. A stable timeperiod is one in which the time period changes very little over a numberof pulsed energy waves. This occurs when conditions that affect sensingassemblage 502 stay consistent or constant. Holding the number of pulsedenergy waves propagating through waveguide 5 to an integer number is aconstraint that forces a change in the time between pulses when thelength of waveguide 5 changes. The resulting change in time period ofeach pulsed energy wave corresponds to a change in aggregate pulseperiods that is captured using digital counter 518 as a measurement ofchanges in external forces or conditions 508.

A further method of operation according to one embodiment is describedhereinbelow for pulsed energy wave 506 propagating from transducer 4 andreceived by transducer 30. In at least one exemplary embodiment, pulsedenergy wave 506 is an ultrasonic energy wave. Transducers 4 and 30 arepiezoelectric resonator transducers. Although not described, wavepropagation can occur in the opposite direction being initiated bytransducer 30 and received by transducer 4. Furthermore, detectingultrasound resonator transducer 30 can be a separate ultrasoundresonator as shown or transducer 4 can be used solely depending on theselected mode of propagation (e.g. reflective sensing). Changes inexternal forces or conditions 508 affect the propagation characteristicsof waveguide 5 and alter transit time 510. As mentioned previously,pulsed system 504 holds constant an integer number of pulsed energywaves 506 propagating through waveguide 5 (e.g. an integer number ofpulsed energy wave time periods) thereby controlling the repetitionrate. As noted above, once pulsed system 504 stabilizes, the digitalcounter 518 digitizes the repetition rate of pulsed energy waves, forexample, by way of edge-detection, as will be explained hereinbelow inmore detail.

In an alternate embodiment, the repetition rate of pulsed energy waves506 emitted by transducer 4 can be controlled by pulse circuit 512. Theoperation remains similar where the parameter to be measured correspondsto the measurement of the transit time 510 of pulsed energy waves 506within waveguide 5. It should be noted that an individual ultrasonicpulse can comprise one or more energy waves with a damping wave shape asshown. The pulsed energy wave shape is determined by the electrical andmechanical parameters of pulse circuit 512, interface material ormaterials, where required, and ultrasound resonator or transducer 4. Thefrequency of the energy waves within individual pulses is determined bythe response of the emitting ultrasound resonator 4 to excitation by anelectrical pulse 520. The mode of the propagation of the pulsed energywaves 506 through waveguide 5 is controlled by mode control circuitry514 (e.g., reflectance or uni-directional). The detecting ultrasoundresonator or transducer may either be a separate ultrasound resonator ortransducer 30 or the emitting resonator or transducer 4 depending on theselected mode of propagation (reflectance or unidirectional).

In general, accurate measurement of physical parameters is achieved atan equilibrium point having the property that an integer number ofpulses are propagating through the energy propagating structure at anypoint in time. Measurement of changes in the “time-of-flight” or transittime of ultrasound pulses within a waveguide of known length can beachieved by modulating the repetition rate of the ultrasound pulses as afunction of changes in distance or velocity through the medium ofpropagation, or a combination of changes in distance and velocity,caused by changes in the parameter or parameters of interest.

It should be noted that ultrasound energy pulses or waves, the emissionof ultrasound pulses or waves by ultrasound resonators or transducers,transmitted through ultrasound waveguides, and detected by ultrasoundresonators or transducers are used merely as examples of energy pulses,waves, and propagation structures and media. Other embodiments hereincontemplated can utilize other waveforms, such as, light.

Measurement by pulsed system 504 and sensing assemblage 502 enables highsensitivity and signal-to-noise ratio as the time-based measurements arelargely insensitive to most sources of error that may influence voltageor current driven sensing methods and devices. The resulting changes inthe transit time of operation correspond to frequency, which can bemeasured rapidly, and with high resolution. This achieves the requiredmeasurement accuracy and precision thus capturing changes in thephysical parameters of interest and enabling analysis of their dynamicand static behavior.

FIG. 7 is a measurement system operating in pulsed mode with digitaloutput according to one embodiment. In particular, it illustrates ameasurement sequence comprising pulse emission into a medium,propagation through the medium, detection of the propagated signal, andmeasurement of the transit time. The medium is subjected to theparameter to be measured such as weight, strain, pressure, wear,vibration, viscosity, and density. In a non-limiting example, pressureis a parameter used to illustrate the measurement system. Pressure isapplied across the medium in a direction of the traversed path of thewaveform. The pressure compresses the medium thereby changing the lengthof the medium. In general, reducing the length of the traversed path bythe pulse correspondingly lowers the transit time of the waveform. Thetransit time is correlated to a pressure measurement in conjunction withthe material properties of the medium. In one embodiment, the transittime is converted to a length, or change in length, of the medium at thetime of the measurement. The material properties of the medium are knownwhere a mathematical function or look up table correlates force orpressure to the measured length or change in length. Further accuracycan be obtained by including any other external conditions (ex.temperature) that affect the medium at the time of the measurement.

The system allows for more than one than one measurement to be taken. Inone embodiment, a new measurement sequence is initiated upon detecting apropagated waveform. A pulse is generated upon detection of thepropagated pulsed energy wave. The pulse is provided to transducer 4 toemit a new pulsed energy wave into the medium. The process continuesuntil stopped under user control. The system provides the benefit ofvery low power usage because as little as a single pulsed energy wavecan be used to make a measurement whereas a continuous wave measurementrequires a continuous signal to be maintained. Reducing the pulse widthcan also lower power usage since only the leading edge is beingdetected. A further benefit is that in a low power application a highenergy pulsed wave can be used to compensate for attenuation in themedium or a significant distance of travel. Although attenuated by themedium, the measurement can be highly accurate and the signaldetectable. The high-energy pulse would be difficult to sustain in lowpower environment (e.g. battery or temporary power source) but in pulsedmode can be used to make measurements that would be difficult usingother methodologies.

Referring to FIG. 2, in pulse mode of operation, the sensing module 101measures a time of flight (TOF) between when a pulsed energy wave istransmitted by transducer 4 and received at transducer 30. The time offlight determines the length of the waveguide propagating path, andaccordingly indicates the change in length of the waveguide 5. Inanother arrangement, differential time of flight measurements can beused to determine the change in length of the waveguide 5. A pulse cancomprise one or more waves. The waves may have equal amplitude andfrequency (square wave pulse) or they may have different amplitudes, forexample, damped or decaying amplitude (trapezoidal pulse) or some othercomplex waveform. The pulsed system detects an edge of each pulsepropagating through the waveguide and holds the delay between theleading edge of each pulse constant under stable operating conditions.

A pulse method facilitates separation of ultrasound frequency, dampingwaveform shape, and repetition rate of pulses of ultrasound waves.Separating ultrasound frequency, damping waveform shape, and repetitionrate enables operation of ultrasound transducers at or near resonance toachieve higher levels of conversion efficiency and power output thusachieving efficient conversion of ultrasound energy. Likewise,separating frequency and repetition rate enables control of dampingfactors within pulses of ultrasound waves by selecting frequencies atsome distance from the resonance points of the ultrasound transducersThis may enable, but is not limited to, lower power operation forultra-low power devices.

The operation of the measurement system will be described utilizing thetiming diagram of FIG. 8. In general, one or more pulsed energy wavescan be propagating through the medium during a measurement. In anon-limiting example, ultrasonic pulsed energy waves are emitted intopropagating structure or waveguide 5 such that three pulsed energy wavesare propagating in the medium. In at least one exemplary embodiment, thesystem maintains the integer number of pulses within waveguide 5 whilethe time period of a pulsed energy wave varies due to external forces orconditions 632 applied to the propagating medium. In one embodiment,external forces or conditions 632 are applied to lengthen or shorten apropagating path of the pulsed energy waves. The time period of eachpulsed energy wave remains constant when multiple measurements are takenand conditions 632 do not vary.

The measurement system comprises a pulsed circuit 608, a switch 604, anamplifier 612, a transducer 4, a waveguide 5, a transducer 30, anamplifier 620, a switch 628, and a digital logic circuit 675. Controlcircuitry 606 can be part of digital logic circuit 675. Switch 604 has afirst terminal coupled to an output 610 of pulse circuit 608, a controlterminal, and a second terminal. Amplifier 612 has an input coupled tothe second terminal of switch 604 and an output. Transducer 4 has aterminal coupled to the output of amplifier 612 and is operativelycoupled for emitting a pulsed energy wave to waveguide 5 at a firstlocation of waveguide 5. Transducer 30 is operatively coupled forreceiving a pulsed energy wave propagated through waveguide 5 at asecond location and generates a signal corresponding to the pulsedenergy wave. In one embodiment, transducer 4 and 30 can both emit andreceive pulsed energy waves thereby allowing transmissionbi-directionally. Amplifier 620 has an input coupled a terminal oftransducer 30 and an output. Switch 628 has a first terminal coupled tothe output of amplifier 620, a control terminal, and a second terminalcoupled to the input of amplifier 612. Digital logic circuit 675 has oneor more outputs for initiating a sensing sequence, taking multiplemeasurements, and measuring the transit time or time period ofpropagated pulsed energy waves.

The timing diagram of FIG. 8 will be referred to in description of pulsemode operation of the measurement system hereinbelow. In particular,pressure or force is measured as an illustration of a parameter beingmeasured. Control circuit 606 initiates a measurement sequence byproviding control signals to switches 604 and 628 respectively indicatedby closed position 842 and open position 846 of FIG. 8. Pulse circuit608 can then be enabled to provide one or more ultrasonic pulsed energywaves to amplifier 612. In the example disclosed above, at least threepulses will be provided by pulse circuit 608 to initiate measurements.In FIG. 8, pulse circuit 608 provides pulses 802, 804, and 806 toamplifier 612. In one embodiment, each time period of the at least threepulses provided by pulse circuit 608 and the corresponding pulsed energywaves emitted into waveguide 5 are approximately equal to ⅓ of thetransit time of a pulsed energy wave propagating from the first locationto the second location of waveguide 5 when no pressure or apredetermined pressure is applied across waveguide 5. As shown in FIG. 8for the example embodiment, the combined length of pulsed energy waves828, 830, and 832 are substantially equal to the length of waveguide 5.

Amplifier 612 receives the pulses from pulse circuit 608 and providesanalog pulses 614 to the terminal of transducer 4. In at least oneexemplary embodiment amplifier 612 comprises a digital driver 642 andmatching network 644. Digital driver 642 and matching network 644transforms the digital output (e.g. square wave) of pulse circuit 608into shaped or analog pulses 614 that are modified for emittingtransducer 4. The repetition rate of pulses 614 is equal to therepetition rate of the pulses provided by pulse circuit 612. Amplifier612 drives transducer 4 with sufficient power to generate energy waves616. In a non-limiting example, energy waves 616 propagating throughwaveguide 5 are ultrasound waves.

In general, ultrasound transducers naturally resonate at a predeterminedfrequency. Providing a square wave or digital pulse to the terminal ofemitting transducer 4 could yield undesirable results. Digital driver642 of amplifier 612 drives matching network 644. Matching network 644is optimized to match an input impedance of emitting transducer 4 forefficient power transfer. In at least one exemplary embodiment, digitaldriver 642, matching network 644, solely, or in combination shapes orfilters pulses provided to the input of amplifier 612. The waveform ismodified from a square wave to analog pulse 614 to minimize ringing andto aid in the generation of a damped waveform by emitting transducer 4.The rounded pulses illustrated in FIG. 8 at the output of amplifier 612are representative of the pulse modification. In one embodiment, apulsed energy wave emitted into waveguide 5 can ring with a dampedenvelope that affects signal detection, which will be disclosed in moredetail below.

The one or more pulsed energy waves 616 propagate through energypropagating structure or waveguide 5 and are detected by detectingtransducer 30. In the example, three pulsed energy waves 822, 824, and826 of FIG. 8 are propagating in waveguide 5 but are in differentlocations within the medium or propagating structure. Pulsed energywaves correspond respectively to pulses 802, 804, and 806. The pulsedenergy wave 822 of FIG. 8 propagates to the second location of waveguide5 and is detected by transducer 30. Transducer 30 generates a signalcorresponding to the received pulsed energy wave that is output toamplifier 620. In general, detecting transducer 30 converts propagatedpulsed energy waves 616 into pulses 618 of electrical waves having thesame repetition rate. The signal output of detecting transducer 30 mayneed amplification. Amplifier 620 comprises pre-amplifier 622 andedge-detect receiver 624. Pre-amplifier 622 receives and amplifiesanalog pulses 618 from transducer 30. Edge-detect receiver 624 detectsan edge of each arriving pulse corresponding to each propagated pulsedenergy wave 616 through waveguide 5. As mentioned previously, eachpulsed energy wave can be a ringing damped waveform. In at least oneexemplary embodiment, edge-detect receiver 624 detects a leading edge ofeach arriving pulse 618. Edge-detect receiver 624 can have a thresholdsuch that signals below the threshold cannot be detected. Edge-detectreceiver 624 can include a sample and hold that prevents triggering onsubsequent edges of a ringing damped signal. The sample and hold can bedesigned to “hold” for a period of time where the damped signal willfall below the threshold but less than the time period between adjacentpulses under all operating conditions.

Amplifier 620 generates a digital pulse 626 that is triggered by eachleading edge of each propagated pulsed energy waves 616 detected bytransducer 30. The first digital pulse output by amplifier 626 isindicated by pulse 808 of FIG. 8. Pulse 808 corresponds to pulsed energywave 828 of FIG. 8. In a non-limiting example, control circuitry 606responds to the first digital pulse output from amplifier 620 afterstarting a measurement sequence by closing switch 628 and opening switch604. The control signals for switches 604 and 628 are respectivelyindicated by control signal 844 and 848. A positive feedback closed loopcircuit is then formed that couples a pulse generated by amplifier 620to the input of amplifier 612 thereby sustaining a sequence comprising:a pulsed energy wave emission into wave guide 5 at the first location;propagation of the pulsed energy wave 616 through waveguide 5; detectionof the pulsed energy wave after traveling to the second locationwaveguide 5; and generation of a digital pulse. Each digital pulse 626is of sufficient length to sustain the pulse behavior of the measurementsystem when it is coupled back to amplifier 612 through switch 628.Alternatively, a measurement process can be stopped by opening switches604 and 628 such that no pulses are provided to amplifier 612 andthereby to transducer 4. In general, circuitry of the measurement systemthat dissipates power can be turned off or put into a sleep mode whendecoupled from amplifier 612 by switches 604 and 628.

In one embodiment, the delay of amplifier 620 and 612 is small incomparison to the propagation time of a pulsed energy wave throughwaveguide 5. In an equilibrium state, an integer number of pulses ofenergy waves 616 in waveguide 5 have equal time periods and transittimes when propagating through the energy propagating structurewaveguide 5. In general, as one energy pulse wave exits (or is detected)at the second location of waveguide 5, a new energy pulse wave isemitted into waveguide 5 (after some finite delay). Movement or changesin the physical properties of the energy propagating structure orwaveguide 5 change the transit time 630 of energy waves 616. Thisdisrupts the equilibrium thereby changing when a pulsed energy wave isdetected by edge-detect receiver 624. A transit time is reduced shouldexternal forces 632 compress waveguide 5 in the direction of propagationof energy waves 616. Conversely, the transit time is increased shouldexternal forces 632 result in waveguide 5 expanding in length. Thechange in transit time delivers digital pulses 626 earlier or later thanprevious pulses thereby producing an adjustment to the delivery ofanalog pulses 618 and 614 to a new equilibrium point. The newequilibrium point will correspond to a different transit time, e.g.different repetition rate with the same integer number of pulses.

Shown in FIG. 8 are pulses 828, 830, and 832 that are emitted intowaveguide 5 by transducer 4 after switch 628 is closed. Transducer 4emits pulses 828, 830, and 832 in response to pulses 808, 812, and 828output by amplifier 820 that respectively correspond to the detection ofpropagated pulsed energy waves 822, 824, and 826 of FIG. 8. Althoughonly three pulsed energy waves are shown in FIG. 8, they will continueto be emitted into waveguide 5 for measurement as long as switch 628remains closed. The transit time of pulses 828, 830, and 832 correspondto the parameter being measured (e.g. force or pressure in the example).In one embodiment, transit time 630 of each pulse can be measured bydigital logic circuit 675 using a high-speed clock and a counter. Forexample, an edge of analog pulse 614 provided to transducer 4 caninitiate a count by the high-speed clock. The generation of a digitalpulse 624 can stop the count and store the number in memory. The countis multiplied by the time period of a clock cycle, which will correspondto the transit time of the pulsed energy wave. The clock can be resetfor the next measurement sequence in response to the digital pulse 624.A similar approach can be deployed measuring a time period of from pulseto pulse output by amplifier 620. A pulse-to-pulse time 856 is indicatedas a time period between pulses 808 and 810 of FIG. 8, which willcorrespond to the time period of the pulsed energy wave 828. Anillustration of a time period 852 of pulse 824 is also provided as anexample.

In another measurement method, the repetition rate of pulses of energywaves 616 during operation of the closed loop circuit, and changes inthis repetition rate, can be used to measure changes in the movement orchanges in the physical attributes of energy propagating structure orwaveguide 5. The changes can be imposed on the energy propagatingstructure or waveguide 5 by external forces or conditions 632 thustranslating the levels and changes of the parameter or parameters ofinterest into signals that may be digitized for subsequent processing,storage, and display. Thus, the repetition rate of pulses of energywaves 616 during the operation of the closed loop circuit, and changesin this repetition rate, can be used to measure movement or changes inphysical attributes of energy propagating structure or medium 5.

The changes in physical attributes of energy propagating structure ormedium 5 by external forces or conditions 632 translates the levels andtranslates the parameter or parameters of interest into a time perioddifference of adjacent pulses or a difference accumulated or averagedover multiple time periods. The time period can be digitized forsubsequent transmission, processing, storage, and display. Translationof the time period into digital binary numbers facilitatescommunication, additional processing, storage, and display ofinformation about the level and changes in physical parameters ofinterest.

Digital logic circuit 675 is described in more detail hereinbelow. Aspreviously mentioned, a first pulse from digital pulses 610 initiates aparameter measurement or sensing of waveguide 5. In at least oneexemplary embodiment, sensing does not occur until initial equilibriumhas been established. Control circuit 606 detects digital pulses 626from amplifier 620 (closing switch 628 and opening switch 604) toestablish equilibrium and start measurement operations. In an extendedconfiguration of pulse-loop mode, a digital block is coupled to thepulsed-loop mode measurement system for digitizing the frequency ofoperation. Translation of the time period of pulsed energy waves intodigital binary numbers facilitates communication, additional processing,storage, and display of information about the level and changes inphysical parameters of interest. During this process, control circuit606 enables digital counter 638 and digital timer 634. Digital counter638 decrements its value on the rising edge of each digital pulse 626output by amplifier 620. Digital timer 634 increments its value on eachrising edge of pulses from clock output 610. A clock such as a crystaloscillator is used to clock digital logic circuit 675 and as a referencein which to gauge time periods of pulsed energy waves. Alternatively,pulse circuit 608 can be a reference clock. A stop signal is output fromdigital counter 638 when the number of digital pulses 626 hasdecremented the value within digital counter 638 to zero. The stopsignal disables digital timer 634 and triggers control logic 606 tooutput a load command to data register 636. Data register 636 loads abinary number from digital timer 634 that is equal to the period of theenergy waves or pulses times the value originally loaded into counter638 divided by a clock period corresponding to oscillator output 610.With a constant clock period, the value in data register 636 is directlyproportional to the aggregate period of the pulsed energy waves orpulses accumulated during the measurement operation. Duration of themeasurement operation and the resolution of measurements may be adjustedby increasing or decreasing the value preset in the count register 640.

This method of operation further enables setting the level of precisionor resolution of the captured data by using long cycle counts tooptimize trade-offs between measurement resolution versus pulserepetition rate, ultrasound frequency, and damping waveform shape, aswell as the bandwidth of the sensing and the speed of the dataprocessing operations to achieve an optimal operating point for asensing module or device that matches the operating conditions of thesystem containing, or subject to, the parameter or parameters ofinterest.

In at least one exemplary embodiment, the sensor system includes thesystem as a wireless module that operates according to one or morecriteria such as, but not limited to, power level, applied force level,standby mode, application context, temperature, or other parameterlevel. Pulse shaping can also be applied to increase reception qualitydepending on the operational criteria. The wireless sensing modulecomprises the pulsed measurement system, one or more sensing assemblies,one or more load surfaces, an accelerometer, electronic circuitry, atransceiver, and an energy supply. The wireless sensing module measuresa parameter such as force/pressure and transmits the measurement data toa secondary system for further processing and display. The electroniccircuitry in conjunction with the sensing assemblies accurately measuresphysical displacements of the load surfaces on the order of a fewmicrons or less along various physical dimensions. The sensing assemblyphysically changes in response to an applied force, such as an appliedload. Electronic circuitry operating in a positive feedback closed-loopcircuit configuration precisely measures changes in propagation time dueto changes in the length of the waveguides; physical length changeswhich occur in direct proportion to the applied force.

In a non-limiting example, an ultrasound signal is used in themeasurement system. For illustration purposes the measurement systemmeasures a load, pressure, or force. The system has two surfaces towhich the measured parameter (e.g. load, pressure, force) can beapplied. In one embodiment, one of the surfaces is in a fixed positionand the measured parameter is applied to the remaining surface.Alternatively, the measured parameter can be applied across bothsurfaces. In one embodiment, the system will measure within a range of3-60 pounds.

The sensing element comprises two piezoelectric transducers and amedium. One or more sensing elements can be used. The sensing element isplaced between the surfaces of the measurement system. In oneembodiment, the waveguide comprises a polymer such as urethane orpolyethylene. In a non-limiting example, the polymer can be stretched orcompressed when subjected to the parameter under measurement and haslittle or no hysteresis in the system. In general, the waveguideefficiently contains and directs an ultrasonic pulsed energy wave suchthat a measurement of either the transit time of the pulsed energy waveto propagate through the waveguide or time period of the pulsed energywave can be taken. The waveguide can be cylindrically shaped having afirst end and a second end of the cylinder. The piezoelectrictransducers are attached at the first and second ends of the waveguideto emit and receive ultrasonic pulsed energy waves. The transducers areattached to be acoustically coupled the waveguide and can have anintermediate material layer to aid in improving the transfer of theultrasonic pulsed energy wave.

In the non-limiting example, the waveguide in a relaxed state is acylinder or column 47 millimeters long which can accommodate one or moreultrasonic pulsed energy waves. The length of the waveguide correspondsto the thickness of the sensor and is thus an indication that a verysmall form factor sensor can be built using this methodology. In oneembodiment, the waveguide is placed in a compressed state in the sensormodule. In the non-limiting example, the waveguide is subjected to aforce or pressure that changes the dimensions of the cylinder. Morespecifically, an applied force or pressure on the surfaces of the systemmodifies the length of the waveguide. In one embodiment, the waveguideis compressed from the 47 millimeter relaxed state to a thickness ofapproximately 39 millimeters. The 39 millimeter compressed statecorresponds to the state where no load is applied to the surfaces of thesensor module.

In the non-limiting example, the emitting piezoelectric transducer has adifferent resonant frequency than the receiving piezoelectrictransducer. The emitting piezoelectric transducer has a resonancefrequency of approximately 8 megahertz. It has a diameter ofapproximately 3.3 millimeters and is approximately 0.23 millimetersthick. The receiving piezoelectric transducer has a resonance frequencyof approximately 10-13 megahertz. It has a diameter of 4 millimeters andis approximately 0.17 millimeters. In one embodiment, the waveguide hasa diameter greater than or equal to the diameter of the largestpiezoelectric transducer. In the example, the waveguide would have adiameter greater than or equal to 4 millimeters.

The sensing module can very accurately measure transit time or a timeperiod of the pulsed energy wave as disclosed hereinabove. In at leastone exemplary embodiment, a single pulsed energy wave can be used totake a measurement thereby minimizing energy usage. Alternatively, morethan one measurement can be taken sequentially, periodically, orrandomly depending on the application requirements. The measured transittime or time period corresponds to the length of the medium orwaveguide. The transit time or time period is correlated to a force orpressure required to compress the waveguide by the measured amount.Preliminary measurements indicate that the sensing module can detectchanges in the length of the waveguide on the order of submicrons. Thus,the sensing module can measure the force or changes in force with highprecision.

Upon reviewing the aforementioned embodiments, it would be evident to anartisan with ordinary skill in the art that said embodiments can bemodified, reduced, or enhanced without departing from the scope andspirit of the claims described below. As an example:

Changing repetition rate or wave composition of complex waveforms tomeasure time delays.

Changing repetition rate of acoustical, sonic, or light, ultraviolet,infrared, RF or other electromagnetic waves, pulses, or echoes of pulsesto measure changes in the parameter or parameters of interest.

FIG. 9 is an exemplary block diagram of the components of a sensingmodule. It should be noted that the sensing module can comprise more orless than the number of components shown. As illustrated, the sensingmodule includes one or more sensing assemblages 903, a transceiver 920,an energy storage 930, electronic circuitry 907, one or more mechanicalsupports 915 (e.g., springs), and an accelerometer 902. In thenon-limiting example, an applied compressive force can be measured bythe sensing module.

The sensing assemblage 903 can be positioned, engaged, attached, oraffixed to the contact surfaces 906. Mechanical supports 915 serve toprovide proper balancing of contact surfaces 906. In at least oneexemplary embodiment, contact surfaces 906 are load-bearing surfaces. Ingeneral, the propagation structure 905 is subject to the parameter beingmeasured. Surfaces 906 can move and tilt with changes in applied load;actions which can be transferred to the sensing assemblages 903 andmeasured by the electronic circuitry 907. The electronic circuitry 907measures physical changes in the sensing assemblage 903 to determineparameters of interest, for example a level, distribution and directionof forces acting on the contact surfaces 906. In general, sensing moduleis powered by the energy storage 930.

As one example, the sensing assemblage 903 can comprise an elastic orcompressible propagation structure 905 between a first transducer 904and a second transducer 914. In the current example, the transducers canbe an ultrasound (or ultrasonic) resonator, and the elastic orcompressible propagation structure 905 can be an ultrasound (orultrasonic) waveguide (or waveguides). The electronic circuitry 907 iselectrically coupled to the sensing assemblages 903 and translateschanges in the length (or compression or extension) of the sensingassemblages 903 to parameters of interest, such as force. It measures achange in the length of the propagation structure 905 (e.g., waveguide)responsive to an applied force and converts this change into electricalsignals which can be transmitted via the transceiver 920 to convey alevel and a direction of the applied force. In other arrangements hereincontemplated, the sensing assemblage 903 may require only a singletransducer. In yet other arrangements, the sensing assemblage 903 caninclude piezoelectric, capacitive, mems, optical or temperature sensorsor transducers to measure the compression or displacement. It is notlimited to ultrasonic transducers and waveguides.

The accelerometer 902 can measure acceleration and static gravitationalpull. It can include single-axis and multi-axis structures to detectmagnitude and direction of the acceleration as a vector quantity, andcan be used to sense orientation, vibration, impact and shock. Theelectronic circuitry 907 in conjunction with the accelerometer 902 andsensing assemblies 903 can measure parameters of interest (e.g.,distributions of load, force, pressure, displacement, movement,rotation, torque and acceleration) relative to orientations of thesensing module with respect to a reference point. In such anarrangement, spatial distributions of the measured parameters relativeto a chosen frame of reference can be computed and presented forreal-time display.

The transceiver 920 comprises a transmitter 909 and an antenna 910 topermit wireless operation and telemetry functions. Once initiated thetransceiver 920 can broadcast the parameters of interest in real-time.The telemetry data can be received and decoded with various receivers,or with a custom receiver. The wireless operation can eliminatedistortion of, or limitations on, measurements caused by the potentialfor physical interference by, or limitations imposed by, wiring andcables connecting the sensing module with a power source or withassociated data collection, storage, display equipment, and dataprocessing equipment.

The transceiver 920 receives power from the energy storage 930 and canoperate at low power over various radio frequencies by way of efficientpower management schemes, for example, incorporated within theelectronic circuitry 907. As one example, the transceiver 920 cantransmit data at selected frequencies in a chosen mode of emission byway of the antenna 910. The selected frequencies can include, but arenot limited to, ISM bands recognized in International TelecommunicationUnion regions 1, 2 and 3. A chosen mode of emission can be, but is notlimited to, Gaussian Frequency Shift Keying, (GFSK), Amplitude ShiftKeying (ASK), Phase Shift Keying (PSK), Minimum Shift Keying (MSK),Frequency Modulation (FM), Amplitude Modulation (AM), or other versionsof frequency or amplitude modulation (e.g., binary, coherent,quadrature, etc.).

The antenna 910 can be integrated with components of the sensing moduleto provide the radio frequency transmission. The substrate for theantenna 910 and electrical connections with the electronic circuitry 907can further include a matching network. This level of integration of theantenna and electronics enables reductions in the size and cost ofwireless equipment. Potential applications may include, but are notlimited to any type of short-range handheld, wearable, or other portablecommunication equipment where compact antennas are commonly used. Thisincludes disposable modules or devices as well as reusable modules ordevices and modules or devices for long-term use.

The energy storage 930 provides power to electronic components of thesensing module. It can be charged by wired energy transfer,short-distance wireless energy transfer or a combination thereof.External power sources can include, but are not limited to, a battery orbatteries, an alternating current power supply, a radio frequencyreceiver, an electromagnetic induction coil, a photoelectric cell orcells, a thermocouple or thermocouples, or an ultrasound transducer ortransducers. By way of the energy storage 930, the sensing module can beoperated with a single charge until the internal energy is drained. Itcan be recharged periodically to enable continuous operation. The energystorage 930 can utilize common power management technologies such asreplaceable batteries, supply regulation technologies, and chargingsystem technologies for supplying energy to the components of thesensing module to facilitate wireless applications.

The energy storage 930 minimizes additional sources of energy radiationrequired to power the sensing module during measurement operations. Inone embodiment, as illustrated, the energy storage 930 can include acapacitive energy storage device 908 and an induction coil 911. Externalsource of charging power can be coupled wirelessly to the capacitiveenergy storage device 908 through the electromagnetic induction coil orcoils 911 by way of inductive charging. The charging operation can becontrolled by power management systems designed into, or with, theelectronic circuitry 907. As one example, during operation of electroniccircuitry 907, power can be transferred from capacitive energy storagedevice 908 by way of efficient step-up and step-down voltage conversioncircuitry. This conserves operating power of circuit blocks at a minimumvoltage level to support the required level of performance.

In one configuration, the energy storage 930 can further serve tocommunicate downlink data to the transceiver 920 during a rechargingoperation. For instance, downlink control data can be modulated onto theenergy source signal and thereafter demodulated from the induction coil911 by way of electronic control circuitry 907. This can serve as a moreefficient way for receiving downlink data instead of configuring thetransceiver 920 for both uplink and downlink operation. As one example,downlink data can include updated control parameters that the sensingmodule uses when making a measurement, such as external positionalinformation, or for recalibration purposes, such as spring biasing. Itcan also be used to download a serial number or other identificationdata.

The electronic circuitry 907 manages and controls various operations ofthe components of the sensing module, such as sensing, power management,telemetry, and acceleration sensing. It can include analog circuits,digital circuits, integrated circuits, discrete components, or anycombination thereof. In one arrangement, it can be partitioned amongintegrated circuits and discrete components to minimize powerconsumption without compromising performance. Partitioning functionsbetween digital and analog circuit enhances design flexibility andfacilitates minimizing power consumption without sacrificingfunctionality or performance. Accordingly, the electronic circuitry 907can comprise one or more Application Specific Integrated Circuit (ASIC)chips, for example, specific to a core signal processing algorithm.

In another arrangement, the electronic circuitry can comprise acontroller such as a programmable processor, a Digital Signal Processor(DSP), a microcontroller, or a microprocessor, with associated storagememory and logic. The controller can utilize computing technologies withassociated storage memory such a Flash, ROM, RAM, SRAM, DRAM or otherlike technologies for controlling operations of the aforementionedcomponents of the sensing module. In one arrangement, the storage memorymay store one or more sets of instructions (e.g., software) embodyingany one or more of the methodologies or functions described herein. Theinstructions may also reside, completely or at least partially, withinother memory, and/or a processor during execution thereof by anotherprocessor or computer system.

FIG. 10, depicts a cross sectional view of a sensing module 1000 infurther detail according to one embodiment. As shown, sensing module1000 includes components of the block diagram of FIG. 9. Sensing module1000 is in a housing that can be made very low profile that includes apower source and telemetry to send data. Notably it can be shaped in avariety of ways such that it can placed or engaged or affixed to orwithin a component or components such that the medium, in this example,a waveguide 1010 is affected by or subjected to the parameter to bemeasured. In the non-limiting example, sensing module 1000 is subjectedto an applied force on the upper and lower surfaces that compresseswaveguide 1010. The amount of compression of waveguide 1010 can bemeasured using the pulse mode technique disclosed herein. The measuredchange in length of waveguide 1010 can be correlated to a pressure orforce based on the material properties of waveguide 1010 (e.g. how muchforce it takes to deform the material per unit length change) and theconditions at the time of the measurement.

In this configuration, the sensing module 1000 can be hermeticallysealed to measure parameters of interest within a wide range ofapplications including, but not limited to, applications within adverseenvironments, long-term applications, or medical applications. It canalso be constructed in a wide range of sizes from very compact to largeas required to fit the application. The hermetic sealing facilitatesreal time measurement and communication of physiological parameterswithin hostile environments.

The sensing module 1000 can be used in applications that requiremeasurement of, but not limited to, load, force, pressure distance,weight, strain, wear, vibration, viscosity, and density, or movement ofportions of physical systems, or load, force, pressure placed upon, ormovement of, physical systems or bodies themselves, or load, force,pressure, or movement caused by external objects in the environment ofthe physical systems or bodies, or combinations of these parameters. Thesensing module 1000 can be ported to applications where the followingattributes are preferred: measurement of parameters of interest in realtime, wired or tethered communication of measured values in real time,exemplary accuracy and precision of measurements, or a wide range ofsizes of the sensing and communication module or device to fitrequirements of applications or environments (e.g., harsh environments,adverse conditions, etc.) within which the measurement data is captured,or any combination of these attributes.

The components of sensing module 1000 comprise the waveguide 1010, theupper piezoelectric transducer 1012 and the lower piezoelectrictransducer 1024. The piezoelectric device can be an ultrasonictransducer, resonator, or other type of transducer such as amicromachined structure. A transducer is a generic term for a devicethat translates energy from one form to another while preserving keyattribute e.g., same frequency, phase, duration, repetition rate. Atransducer is a device that is actuated by power from one system andthat supplies power usually in another form to a second system, forexample, a loudspeaker.

The minimum thickness of sensing module 1000 comprises a stack of upperpiezoelectric transducer 1012, waveguide 1010, and lower piezoelectrictransducer 1024. In the embodiment, one or more transducer/waveguidestacks are used. The location where the pressure or force is applied ontop cover 1002 can be determined by operatively locating three stacksaround a contact area. Differences in pressure measurements from thethree stacks can determine the location. For example, pressure appliedin the center between the stacks will result in equal pressure readings(e.g., the contact area is centered). Conversely, different pressurereadings between the three stacks will move the contact area closertowards the higher reading and farther from the stack with the lowestreading. An upper portion of sensing module 1000 comprises stacks,flexible interconnect, spring retainers 1006, and spring posts 1014. Theupper portion of sensing module 1000 resides between top steel plate1004 and printed circuit board 1018. A cup 1020 is the support structurefor sensing module 1000. Cup 1020 supports printed circuit board 1018.Cup 1020 includes cavities for housing circuitry on a lower surface ofprinted circuit board 1018. A top cover couples to cup 1020 covering topsteel plate 1004.

As previously indicated, accurate measurements of the amplitude andposition of the load are achieved by measuring propagation time ofultrasonic waves or pulses within the flexible waveguide 1010 (orwaveguides as other embodiments will include multiple springs andwaveguides). The relationship of the propagation of ultrasound in amedium with respect to the aspect ratio of the piezoelectric element iswell known. Ultrasound waves propagate linearly through the waveguidethus maintaining an accurate relationship between compression orextension and transit time of ultrasound waves. This enables accurateconversion of mechanical changes in the length or compression orextension of the waveguide into changes in the transit time ofultrasound waves or pulses within the waveguide. Moreover, upperpiezoelectric transducer 1012, lower piezoelectric device 1024 andwaveguide 1010 in conjunction with the mechanical supports (e.g.,biasing springs) are uniquely calibrated by design to produce specificmeasurable and deterministic physical response to load or displacement.

FIG. 11 is a communication network 1100 for sensing applications inaccordance with an exemplary embodiment. Briefly, the communicationnetwork 1100 expands the sensing system 1155 of FIG. 9 to provide broaddata connectivity to other devices or services. As illustrated, thesensing system 1155 can be communicatively coupled to the communicationsnetwork 1100 and any associated systems or services.

As one example, the sensing system 1155 can share its parameters ofinterest (e.g., distributions of load, force, pressure, displacement,vibration, viscosity, movement, rotation, torque and acceleration) withremote services or providers, for instance, to analyze or report on astatus or outcome. The communication network 1100 can further be tied toa records system to implement rigorous information technology practices.In general, the sensing system can be linked to different informationtechnology systems and software applications to communicate, to exchangedata accurately, effectively, and consistently, and to use the exchangeddata.

The communications network 1100 can provide wired or wirelessconnectivity over a Local Area Network (LAN) 1101, a Wireless Local AreaNetwork (WLAN) 1105, a Cellular Network 1114, and/or other radiofrequency (RF) system. The LAN 1101 and WLAN 1105 can be communicativelycoupled to the Internet 1120, for example, through a central office. Thecentral office can house common network switching equipment fordistributing telecommunication services. Telecommunication services caninclude traditional POTS (Plain Old Telephone Service), cellularnetworks, and broadband services such as cable, HDTV, DSL, VoIP (Voiceover Internet Protocol), IPTV (Internet Protocol Television), Internetservices, and so on.

The communication network 1100 can utilize common computing andcommunications technologies to support circuit-switched and/orpacket-switched communications. Each of the standards for Internet 1120and other packet switched network transmission (e.g., TCP/IP, UDP/IP,HTML, HTTP, RTP, MMS, SMS) represent examples of the state of the art.Such standards are periodically superseded by faster or more efficientequivalents having essentially the same functions. Accordingly,replacement standards and protocols having the same functions areconsidered equivalent.

The cellular network 1114 can support voice and data services over anumber of access technologies such as GSM-GPRS, EDGE, CDMA, UMTS, WiMAX,2G, 3G, WAP, software defined radio (SDR), and other known technologies.The cellular network 1114 can be coupled to base receiver 1110 under afrequency-reuse plan for communicating with mobile devices 1102.

The base receiver 1110, in turn, can connect the mobile device 1102 tothe Internet 1120 over a packet switched link. The internet 1120 cansupport application services and service layers for distributing datafrom the sensing system 1155 to the mobile device 1102. The mobiledevice 1102 can also connect to other communication devices through theInternet 1120 using a wireless communication channel.

The mobile device 1102 can also connect to the Internet 1120 over theWLAN 1105. Wireless Local Access Networks (WLANs) provide wirelessaccess within a local geographical area. WLANs are typically composed ofa cluster of Access Points (APs) 1104 also known as base stations. Thesensing system 1155 can communicate with other WLAN stations such aslaptop 1103 within the base station area. In typical WLANimplementations, the physical layer uses a variety of technologies suchas 802.11b or 802.11g WLAN technologies. The physical layer may useinfrared, frequency hopping spread spectrum in the 2.4 GHz Band, directsequence spread spectrum in the 2.4 GHz Band, or other accesstechnologies, for example, in the 5.8 GHz ISM band or higher ISM bands(e.g., 24 GHz, etc).

By way of the communication network 1100, the sensing system 1155 canestablish connections with a remote server 1130 on the network and withother mobile devices for exchanging data. The remote server 1130 canhave access to a database 1140 that is stored locally or remotely andcan contain application specific data. The remote server 1130 can alsohost application services directly, or over the internet 1120.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. A low power measurement system for measuring aparameter comprising: a medium where the parameter to be measuredaffects the medium; a first transducer coupled to the medium at a firstlocation where the first transducer emits a pulsed energy wave into themedium in response to a pulse; a second transducer coupled to the mediumat a second location where the pulsed energy wave propagates through themedium to the second location and where the second transducer generatesa signal in response to the pulsed energy wave; and a pulsed systemincluding: an edge detect circuit for detecting an edge of the signalfrom the second transducer; and a first pulse circuit for generating apulse to initiate a subsequent measurement sequence in response to adetected edge by the edge detect circuit where a transit time of thepulsed energy wave propagating from the first location to the secondlocation is measured and the transit time or change in transit timecorresponds to the parameter where the system includes an amplifierhaving an input coupled to an output of the edge detect circuit and anoutput coupled to the first transducer.
 2. The system of claim 1 where asensor form factor comprises a stack of the first transducer coupled toa first surface of a waveguide and the second transducer coupled to thesecond surface of the waveguide.
 3. The system of claim 1 where theamplifier includes circuitry to dampen a wave shape for optimaltransmission and reception in accordance with a matched network.
 4. Thesystem of claim 1 where the pulsed energy wave is a damped ringingwaveform and where the edge detect circuit detects a leading edge of thesignal from the second transducer and where upon detecting the leadingedge of the signal, the edge detect circuit is disabled from edgedetecting for a predetermined period of time.
 5. The system of claim 4where the transit time corresponds a time measured from the pulseprovided to the first transducer to the detected edge of the signal fromthe second transducer.
 6. The system of claim 5 further including asecond pulse circuit for providing one or more pulses to the firsttransducer to initiate a sensing process where the second pulse circuitis decoupled from the first transducer when the edge detect circuitdetects an edge of a first pulsed energy wave.
 7. The system of claim 6where the first pulse circuit is coupled to the first transducer toprovide the pulse to initiate the next measurement sequence when thesecond pulse circuit is decoupled from the first transducer.
 8. Thesystem of claim 7 where the pulsed system modulates a time period ofpulsed energy waves as a function of changes in distance or velocitythrough the medium.
 9. The system of claim 8, further comprising adigital block for digitizing the frequency of operation of the pulsedsystem where the frequency corresponds to a time period of one or morepulsed energy waves.
 10. The system of claim 1 where the pulsed systemis configured to operate wirelessly according to one or more operationalcriteria comprising power level, applied force level, standby mode,application context, temperature, or other parameter level.
 11. Thesystem of claim 1, where a change in length of the medium generates acorresponding change in transit time that is converted to a forceapplied thereto.
 12. The system of claim 1 where the medium comprisesbone.
 13. A method of measuring a parameter comprising the steps of:emitting pulsed energy waves into a first location of a medium with afirst transducer; detecting pulsed energy waves at a second location ofthe medium with a second transducer where the step of detecting furtherincludes the steps of: generating a pulse with an edge detect circuitfrom a signal provided by the second transducer responsive to eachpulsed energy wave at the second location; shaping each pulse with anamplifier; impedance matching for efficient transfer of each shapedpulse to the first transducer; and coupling each shaped pulse to thefirst transducer where the first transducer emits a pulsed energy waveinto the medium in response to each shaped pulse; maintaining more thanone pulsed energy wave in a the medium subjected to the parameter beingmeasured; initiating measurement by providing a fixed integer number ofpulse energy waves to the medium using a counter; measuring the transittime of the fixed integer number of pulsed energy waves with a timer;and relating the transit time and material properties of the medium tothe parameter being measured.
 14. The method of claim 13 furtherincluding a step of maintaining a fixed integer number of pulsed energywaves in the medium during measurement of the parameter.